Safety sensitive automobile components such as wheel bolts and wheel nuts for motor vehicles must meet strict requirements with regard to corrosion and wear resistance as well as to friction properties. Such automobile parts are exposed to severe outdoor environments including road water and rock salt and, hence, are required to have high degrees of corrosion resistance, impact strength and mechanical wear resistance. Furthermore, automobile wheel bolts and wheel nuts undergo severe temperature changes during the operation of an automobile. Hence, it is required that such bolts and nuts do not loosen when they undergo temperature changes and, at the same time, the thread does not become stuck due to corrosion. Generally, the automobile industry requires that bolts and nuts for this purpose have a total coefficient of friction μtotal as determined by DIN 946 of the German Institute for Standards of 0.05 to 0.18. Furthermore, it is required that this value remains substantially constant even after several times of fastening and loosening. In addition, the automobile industry requires that the loosening torque of such bolts and nuts remain in a specified range when the part is heated to different temperatures. Bolts and nuts without protective coating do not meet such requirements. It is, therefore, necessary that the bolts and nuts be so coated as to resist both chemical corrosion and mechanical damage or wear and as to exhibit the required friction properties.
Furthermore, environmental regulations require manufacturers of automobiles to significantly reduce or even eliminate the amount of environmentally incompatible substances in automobiles. On the list of substances that are considered environmentally incompatible is hexavalent chromium, a substance that is conventionally employed in galvanization processes used for imparting anti-corrosion properties to automobile parts. It is, therefore, desirable to produce bolts and nuts for automobiles that do not contain any environmentally incompatible substances such as hexavalent chromium.
In addition, the automotive industry has enormous quantity demands, as in the case of nuts and bolts. Hence, it is essential that any method of manufacturing bolts and nuts has a high production capacity that can meet the quantity demands of the automotive industry.
Conventional wheel bolts and wheel nuts for use in automobiles contain chromium (VI) based coating systems. Such conventional wheel bolts and wheel nuts generally contain a protective coating of the following type: (a) a Zn or Zn/Ni layer; (b) a chromium (VI) based layer; and (c) a lubricant layer. While such systems have acceptable corrosion, wear and friction properties, the disadvantage of chromium (VI) based systems is their environmental incompatibility.
Silicates have been used in electrocleaning operations to clean steel, tin, among other surfaces. Electrocleaning is typically employed as a cleaning step prior to an electroplating operation. Using “Silicates as Cleaners in the Production of Tinplate” is described by L. J. Brown in February 1966 edition of Plating; hereby incorporated by reference.
Processes for electrolytically forming a protective layer or film by using an anodic method are disclosed by U.S. Pat. No. 3,658,662 (Casson, Jr. et al.), and United Kingdom Patent No. 498,485; both of which are hereby incorporated by reference.
U.S. Pat. No. 5,352,342 to Riffe, which issued on Oct. 4, 1994 and is entitled “Method and Apparatus for Preventing Corrosion of Metal Structures”, describes using electromotive forces upon a zinc solvent containing paint; hereby incorporated by reference.
The instant invention solves problems associated with conventional fastening elements by providing an article such as wheel bolt or a wheel nut for use in automobiles that has improved corrosion, wear, and friction properties and is environmentally acceptable. Further benefits of the invention will become apparent from a consideration of the ensuing description and drawings.